1. Field of the Invention
The present invention relates to image forming apparatuses such as electrophotographic copying machines and printers, and particularly relates to an image forming apparatus, which can perform preliminary processing in such a case that the image forming operation of the image forming apparatus is disabled, for example, due to jamming or another trouble, and more specifically can perform the preliminary processing for normally or accurately performing the subsequent image formation before the disabled image forming apparatus is enabled to perform the image forming operation.
2. Description of the Background Art
In an electrophotographic image forming apparatus such as a full-color copying machine, a toner image corresponding to an original image is formed on a record sheet, for example, in the following manner. An image reader reads the image on an original document which is located at a predetermined position. Based on original image information thus read, electrostatic latent images which correspond to several colors (e.g., cyan, magenta, yellow and black) of the original image, respectively, are formed on an electrostatic latent image carrier such as a photosensitive member. Every time the electrostatic latent image corresponding to one of the colors is formed, development is performed by a developing device, which accommodates toner of the same color, to form a toner image of the same color on the electrostatic latent image carrier. The toner image thus formed is transferred onto the sheet carried on a sheet carrying member such as a transfer drum. In this manner, the toner images of the respective colors corresponding to the original image are formed on the sheet in a superposed fashion. Usually, the toner images on the sheet are fixed thereto by a heat, pressure or the like.
This copying machine may attain such states that the copying cannot be performed, or the copying operation is disabled due to a certain reason. These states will be referred to as the copying disabled state, hereinafter. Before the copying machine is restored from the copying disabled state to a copying enabled state in which execution of the copying operation is enabled, preliminary processing, which will be described later, may be performed for normally or accurately performing the copying operation before a subsequent copying operation is executed. A copying machine which can perform such preliminary processing before enabling the copying operation has been proposed.
When power switch of the copying machine is off, the copying machine is usually disabled. Also, a sheet may be jammed within the copying machine during transportation for the copying operation. Further, the machine may detect that the sheet is not correctly carried on the sheet carrying member such as a transfer drum during copying, or that a rotary member (e.g., the photosensitive drum or the transfer drum) to be driven does not operate correctly during the copying. In these states, the copying machine stops the copying operation, and is set to the copying disabled state. Even during a period for which the copying is not being performed, the copying machine is usually disabled when a certain trouble is detected. Troubleshooting is performed as follows. For example, in the case of jamming, a cover or door of the copying machine is opened for removing the jammed sheet. If the cover or the like is left open even after removal of the jammed sheet or other recovery processing, the copying machine is usually disabled because one may receive an electric shock by touching a portion carrying a high voltage, or may burn himself or herself by touching a hot portion.
More specifically, the preliminary processing performed by the copying machine described above may be performed as described in the following items (1)-(3).
(1) Processing is performed to determine whether a remaining sheet is present on the sheet carrying member such as a transfer drum for preventing such a state that the record sheet is not correctly held on the sheet carrying member such as a transfer drum during the next copying and is jammed thereon due to the sheet remaining on the sheet carrying member. For this purpose, a sensor or the like is usually arranged at a fixed position opposed to the surface of the sheet carrying member for determining whether a sheet is present on the surface of the sheet carrying member such as a transfer drum. However, the sheet is usually carried on the sheet carrying member without fully covering the entire surface thereof. Therefore, the sheet remaining on the sheet carrying member may not be detected in some cases. For preventing such failure in detection, the carrying member is, for example., driven to rotate for reliably detecting the residual sheet.
(2) Processing is performed to form a toner pattern on the electrostatic latent image carrier such as a photosensitive drum, which is driven to rotate, under predetermined image forming conditions. The density of the toner pattern is detected by an AIDC sensor or the like, and the detected density is used to determine the image forming conditions for the next copying operation such as a developing bias voltage in the developing device, and a quantity of laser beams emitted from a laser device for emitting the laser beams onto the electrostatic latent image carrier to form the electrostatic latent image. These conditions are determined to attain an appropriate density of the toner image formed on the record sheet in the next copying operation and, in other words, to prevent an excessively large or small density.
(3) Processing is performed to remove toner which adhered onto the surface of the sheet carrying member such as a transfer drum as a result of the copying operation. This processing is performed for preventing smearing of the sheet by the adhered toner in the next copying operation. Usually, removal of the toner for preventing smearing of the sheet in the next copying operation is performed at the last step in the copy sequence when the copying is correctly completed without any trouble. If the copying operation is interrupted due to a trouble or the like, this removal processing is not performed, and therefore the above preliminary processing is performed for the next copying operation.
The copying machine starts the above kinds of preliminary processing, for example, after it is powered on or after a cover, door or the like which was opened for recovery from the trouble or the like is closed.
As described above, the foregoing kinds of preliminary processing (1)-(3) are performed in the copying machine before the next copying operation is enabled again so that the next copying can be performed normally and correctly by removing the cause of trouble disabling the copying operation. This copying machine cannot start the copying operation until completion of the preliminary processing, and a user must wait for a certain time until the machine to be enabled, which impedes easy use and operation.
The above description has been given on the copying machine provided with the sheet carrying member such as a transfer drum. Similar problems may arise in image forming apparatuses such as a printer other than the copying machine, apparatuses such as a copying machine and a printer not provided with a sheet carrying member (e.g., a transfer drum), and image forming apparatuses such as a copying machine and a printer provided with intermediate transfer members, if these apparatuses perform the preliminary processing for the above purposes.